Intermittent sprinkler and system

ABSTRACT

A system of pressure actuated intermittent discharge sprinkler units, in which each unit is adapted to be installed below grade level and includes an accumulator for connection to a source of water for accumulating water under increasing pressure, a pressure actuated sprinkler head connected to the accumulator and having a normally closed valve means carried by a nozzle assembly, such that the valve means responds to increasing water pressure in the accumulator and intermittently opens raising the nozzle assembly above grade level to discharge water therefrom, and a self-adjusting flow control valve connecting the accumulator to a source of water such that the periodic build-up and release of pressure in each unit accumulator does not adversely influence the operation of the remaining sprinkler units connected to the same water source. The nozzle assembly which is formed with a radially directional nozzle includes a ratchet indexing means for cyclically and incrementally rotating the nozzle assembly each time it is raised and subsequently lowered by the periodically changing water pressure in the accumulator. The nozzle assembly desirably includes a secondary or auxiliary nozzle, spaced below the principal nozzle, and adapted to deliver water to a substantially smaller radius than the effective radius of the principal nozzle. The auxiliary nozzle also serves to discharge the upper portion of water collecting in a bowl or skirt which houses the valve means and nozzle assembly, thereby preventing such water from overflowing the bowl and creating a muddy ring immediately adjacent to the bowl.

United States Patent Feb. 26, 1974 Wilson INTERMITTENT SPRINKLER AND SYSTEM [75] Inventor: John D. Wilson, Balboa, Calif. [73] Assignee: Williamson-Built, Inc., Santa Fe Springs, Calif.

[22] Filed: May 26, 1972 [21] Appl. No.: 257,741

[52] US. Cl. 239/206 [51] Int. Cl B05b 3/00, B05b 15/10 [58] Field of Search 239/204, 205, 206, 238

[56] References Cited UNITED STATES PATENTS 2,393,091 l/l946 Lacy-Mulhall 239/206 2,744,786 5/1956 Whitehead 239/206 Primary Examiner-Lloyd L. King Attorney, Agent, or FirmMiketta, Glenny, Poms & Smith sprinkler head connected to the accumulator and having a normally closed valve means carried by a nozzle assembly, such that the valve means responds to increasing water pressure in the accumulator and intermittently opens raising the nozzle assembly above grade level to discharge water therefrom, and a selfadjusting flow control valve connecting the accumulator to a source of water such that the periodic buildup and release of pressure in each unit accumulator does not adversely influence the operation of the remaining sprinkler units connected to the same water source. The nozzle assembly which is formed with a radially directional nozzle includes a ratchet indexing means for cyclically and incrementally rotating the nozzle assembly each time it is raised and subsequently lowered by the periodically changing water pressure in the accumulator. The nozzle assembly desirably includes a secondary or auxiliary nozzle, spaced below the principal nozzle, and adapted to deliver water to a substantially smaller radius thanthe effective radius of the principal nozzle. The auxiliary nozzle also serves to discharge the upper portion of water collecting in a bowl or skirt which houses the valve means and nozzle assembly, thereby preventing such water from overflowing the bowl and creating a muddy ring immediately adjacent to the bowl.

18 Claims, 15 Drawing Figures PATENTED FEB26 I974 SHEET 1 BF 4 INTERMITTENT SPRINKLER AND SYSTEM BACKGROUND AND SUMMARY OF THE INVENTION In general the present invention relates to sprinkler systems and more particularly to a system in which each sprinkler head is pressure-actuated for intermittent water discharge.

Conventional sprinklers apply water at a relatively high and continuous rate. This characteristic leads to problems in designing an efficient and effective irrigational sprinkler system. Because of the high rate or intensity of the water delivered by conventional sprinkler heads, run-off and leaching of the ground are likely to result, since the soil is only capable of absorbing water at a substantially slower rate. The time available for an optimum irrigating cycle is typically several hours, yet conventional sprinkler heads and systems deliver the total amount of water required during such cycles in a matter of minutes. Accordingly, in these conventional systems provision must be made for actuating each sprinkler in the systems for a short interval during the irrigating cycle. This is accomplished with manually operated quick-coupler valves or with an automated control system including electrical timers, switches, relays, control wiring and remote control valves. Both approaches are expensive, the former in terms of labor time and the latter by reason of the cost of equipment. Furthermore, systems which employ automatic controllers have been found generally unreliable, probably an inherent characteristic resulting from their complexity. The cost of maintaining one of these automatic systems is quite high, since they are subject to failure not only in the controllers, valve and sprinkler heads but also in the control wiring buried in the ground. For example it has been found that these systems are susceptible to damage by lightning Still another disadvantage of these presently used systems is in their requirements of a substantial supply or delivery rate to each of the sprinkler heads in order to support the relatively high water discharge rate thereat. This high delivery rate is required even though each sprinkler head may be operated only for a short interval, as dictated by the irrigation cycle. Nevertheless, since the discharge during this interval is continuous, the high flow rate must be sustained, and this in turn necessitates more expensive pumping and piping capacity. The high flow rate demands on the water supply also result in complicating the watering schedules in that overlap conflicts can occur between two or more automatic controllers, which if turned on at the same time result in an excessive demand on the water supply system. This in turn results in a reduced flow to the affected sprinklers thereby leaving large ground portions unirrigated.

In general it is an object of the present invention to avoid the foregoing disadvantages associated with conventional sprinkler or irrigation systems by providing a sprinkler head and system in which the water delivery to the ground is intermittent rather than continuous, and the flow of water from the source is continuous during operation. Prior efforts along these lines have been attempted as exemplified by U. S. Pat. No. 3,32 l l 38 to Curry, U. S. Pat. No. 1,998,592 to Schenk and German Pat. No. l,044,496 to Moser. One reason why such previous attempts have not been successful concerns their lack of any means to accurately control the delivery rate to the individual pressure actuated sprinkler heads in a system comprising a plurality of such heads. These prior approaches have employed a throttling device, such as a fixed restricted orifice to control the frequency of the water discharge. Thus by using a throttling device, the rate of water flow or admittance into an accumulator associated with one of these earlier devices is variable, the rate increasing or decreasing as the amount of water in the accumulator changes, thus decreasing or increasing the water pressure therein. This results in a constantly changing demand on the water supply system causing a fluctuating pressure in the supply line which interferes with the operation of the remaining sprinkler heads in the system. If one sprinkler in such a system is found to be delivering too little water, increasing the delivery rate to its accumulator will result in a reduced delivery rate to the other sprinkler unit. This problem of balancing the system and being unable to provide head-to-head control over the various sprinklers has rendered such prior intermittent discharge sprinklers unsuccessful for large scale applications, for example on a golf course. Of course, where only one sprinkler is required, for example the home use sprinkler as illustrated in the Curry US. Pat. No. 3,321,138, this system balancing problem does not exist.

Furthermore, most of these prior intermittent discharge sprinklers are not adapted for permanent installation in an environment, such as a golf course, where the sprinkler must be disposed so as not to be an obstacle to the players or to lawn manicuring equipment. Additionally this installation requirement must be met in conjunction with a sprinkler head capable of delivering water at substantial distances, such as a foot radius 'per head.

Accordingly it is one object of the present invention to provide an intermittent sprinkler head and system capable of covering a large area per head and yet requiring a relatively low and constant rate of water flow to each head. An advantage of this sprinkler system is its ability to deliver water to the soil at a rate commensurate with the soil's ability to absorb water. This in turn provides a further advantage in that the total water usage rate for the entire system is reduced to a minimum, and allows for concurrent operation of all the sprinklers associated with one system. The need for manual or automatic control of the individual sprinklers is eliminated. A further object of the present invention is to provide such a sprinkler head and system capable of being permanently installed in environments where the sprinkler heads must not offer obstructions to ground maintenance equipment.

It is an advantage of the present invention that each discharge sprinkler requires only a relatively low volume flow rate for operation such that the size of piping and the capacity of the pumping equipment is minimized thus reducing the installation cost of the system. Further advantages of the intermittent sprinkler of the present invention are that, once installed, it is automatically actuated merely by a straightforward manual or automatic control of the main water line; that it is a relatively simple device and inherently reliable; and that it is designed such that no water hammer occurs and no pressure fluctuations are communicated to the main water line.

These and further objects and advantages of the sprinkler and system of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of an exemplary embodiment thereof. Reference will be made to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a composite schematic and vertical sectional view of a system in accordance with the present invention, including a sprinkler unit with the parts in retracted position; and an accumulator, partially in section to show the diaphagm in solid lines in its lowermost position, and in dotted outline in its uppermost position; other similar units are schematically shown, together with a pump, a controlling timer and piping interconnecting the several units making up a system;

FIGS. 2A and 2B are fragmentary vertical sectional views, on an enlarged scale, of a preferred form of a flow control valve used in the invention, respectively showing the valve in its maximum and minimum flow rate positions, in response to pressure differential across the valve.

FIG. 3 is an enlarged fragmentary sectional view of the valve mechanism of the sprinkler head, taken along lines III-Ill of FIG. 1 thereof;

FIG. 4 is a fragmentary sectional view illustrating the sprinkler head during active water discharge;

FIG. 5 is a fragmentary vertical sectional view of the sprinkler head similar to FIG. 4 except illustrating the head as it approaches retracted position;

FIG. 6 is a fragmentary top plan view taken from arrows VI-VI of FIG. 5, the cover plate being partially cut away for clarity;

FIG. 7 is a sectional view taken along the arrows VII- \/II of FIG. 4'.

FIG. 8 is a sectional view taken along the plane VIII- VIII of FIG. 5;

FIG. 9 is a diagrammatic showing of the indexing mechanism of the head;

FIG. 10 is a sectional view taken along the plane X-X of FIG. 5, with the rotatable parts rotated substantially 90 counter-clockwise as seen in FIG. 10;

FIGS. 11, 12, I3 and 14 are fragmentary side elevational views, with the lower portion of the bowl shown in section, illustrating the rotation or indexing mechanism carried by sprinkler head 11 during various operating conditions as viewed from XIXI of FIG. 10.

DETAILED DESCRIPTION With reference to FIG. 1, the present invention provides a system of pressure actuated intermittent discharge sprinkler units, such as units l6, l7 and 18, connected to a common water source in this instance provided by a water line 13. In detail, unit 16 includes a sprinkler head indicated generally at 11, a gas biased water accumulator 12 having an upper chamber 22 adapted to be precharged with gas to a desired pressure and separated by a diaphram from an expandable volume lower chamber 23 communicating via conduit 24 with flow control valve 14 to receive water from line 13 such that lower chamber 23 expands with an increasing volume of water thereby decreasing the volume of chamber 22 and increasing the gas pressure therein. A pressure actuated sprinkler head 11 including a normally closed spring biased valve means, here in the form of poppet valve 26, is connected to chamber 23 of accumulator 21 through a conduit 27 and conduit 24. The spring biased valve means including poppet valve 26 of each sprinkler head 11 is disposed to respond to increasing water pressure in accumulator 12, caused by the increase in gas pressure in upper chamber 22, to open against the spring bias and discharge water through a nozzle as best illustrated in FIG. 4 relieving the pressure in accumulator 12 and thus subsequently returning to its normally biased closed condition.

While sprinkler system including an accumulator and pressure actuated discharge head operating generally in this manner are known, the present invention provides an improved cooperation between these components and between the remaining pressure actuated units, such as unit 17 and 18 by the provision of flow control valve 14. Valve 14 regulates the flow, volume per unit time, of water into accumulator 12 such that a constant flow is achieved notwithstanding the periodic variation in the water pressures within chamber 23 of accumulator l2 and within conduits 24 and 27 because of the intermittent actuation of head 11. Whereas in previous systems the source of water, such as water line 13, would fluctuate in pressure in accordance with the periodic increase and decrease of water pressure within chamber 23 of accumulator 12, the present invention substantially eliminates the influence of each discharge unit, such as unit 16 on the available water supply. In this manner the remaining discharge sprinkler units, such as units 17 and 18 connected to source 13, operate from a constant water supply pressure and thus each may be individually adjusted for maximum efficiency and proper ground coverage.

Although flow control valve 14 may be provided by any of several known devices, one commercially available unit utilizing a resilient annulus 28 defining as best shown in FIGS. 2A and 28 a variable cross section orifree 29 in response to the differential pressure across the device has been found particularly suited for this application. This device, available from the Dole Division of Eaton Yale and Towne, Inc. Morton Grove, Ill., may be purchased in several sizes and provides a self adjustment between a relatively large orifice 29 when an inlet pressure Pl approaches an outlet pressure P2 as shown in FIG. 2A, to a more constricted orifice 29 as shown in FIG. 28 where the outlet pressure P2 is substantially less than the inlet pressure P1. Accordingly, in the combination in the present invention annulus 28 of flow control valve 14 assumes its restricted condition when the inlet pressure P1 is substantially greater than the pressure within chamber 23 of accumulator 12. As the pressure within chamber 23 increases with the flow of water into accumulator 12, the outlet pressure P2 of the flow control valve increases until it approaches the inlet pressure such that the orifree 29 expands allowing the same flow rate of water under the conditions of a lower differential inlet to outlet pressure. This type of flow control valve is more fully disclosed in U.S. Pat. Nos. 2,389,134 and 2,454,929.

Although in the illustration of FIG. 1, flow control valve 14 is shown jointly connected to conduits 24 and 27 communicating with accumulator 12 and head 11 respectively, it will be appreciated that head 11 may alternatively be connected directly to chamber 23 of ac cumulator 12 through another opening therein so long as head 11 freely communicates with the water chamber 23 of the accumulator. Similarly, flow control valve 14 could be connected individually and directly to chamber 23 of accumulator 12 from supply line 13 so long as valve 14 is not disposed serially within the discharge path between the accumulator and the head.

Further in accordance with the present invention each pressure actuated intermittent discharge sprinkler head 11 is comprised of an upstanding pipe member 31, best shown in FIG. 4, having a throat opening 32 at an upper end of member 31 and adapted at a lower end for connection to a source of water under pressure. Such connection is in this instance by means of a lower pipe extension 33 also vertically disposed and connected to communicate with conduit 27 as illustrated in FIG. 1. Thus pipe extension 33 and pipe member 31 define a vertically disposed passage upwardly from conduit 27 to throat opening 32. A nozzle assembly 34 is provided having a sleeve member 36 slidably and rotatably mounted on pipe member 31 adjacent throat opening 32'for vertical reciprocation of nozzle assembly 34 between a retracted position as shown in FIG. 1 and an extended position as shown by FIG. 4. A directional nozzle means including a primary nozzle 37 and a secondary nozzle 38 are formed by assembly 34 adjacent an upper and closed end 39 of sleeve member 36 for communication with throat opening 32 of pipe member 31 and discharge of water outwardly in radially directional streams as shown by FIG. 4. In order to provide selective opening and closing of throat opening 32, a valve means in the form of poppet valve 26 is carried by assembly 34 for vertical reciprocation therewith between a retracted position as it is shown in FIG. 1 with valve 26 closing the opening 32 and an extended position vertically spaced from the retracted position so as to communicate throat opening 32 with nozzles 37 and 38 for water discharge as shown in FIG. 4. To achieve this joint movement, poppet valve 26 is fastened to upper end 39 of sleeve 36 by means of a rod 41 coaxially threaded to valve 26 and extending upwardly therefrom through an opening in closed end 39 and secured there by a nut 42 threaded on rod 41 for tightening a lower shoulder 43 of nut 42 against an upper abutment 44 of enclosed end 39 with an annular washer seal 46 interposed therebetween.

Nozzle assembly 34 and poppet valve 26 are jointly biased in the retracted position with throat opening 32 closed by means here in the form of an elongate coiled spring 47 coaxially mounted within pipe member 31 and being connected between valve 26 and member 31 to provide a spring bias continuously urging nozzle assembly 34 to the retracted position. An upper end 48 of spring 47 is disposed so as to circumferentially abut a downwardly facing circumferential flange 49 fixed relative to pipe member 31 underlying throat opening 32 while a lower end 51 of the spring is connected to valve 26 by a linkage means here in the form ofa lower integral extension of rod 14 and a bracket 52 threaded to rod 41 with the rod upwardly extending therefrom to its threaded engagement with valve 26 as best illustrated in FIG. 4.'Bracket 52 is formed with an annular flange portion 53 providing an upwardly facing abutment for the lower end 51 of spring 47 and being connected to a portion 54 threaded to rod 41 by means of a plurality of circumferentially spaced struts 56 providing in cooperation with an annular opening 57in flange 53 for the free flow of water upwardly toward throat opening 32 as illustrated by arrow 58 in FIG. 4. Spring 47 is placed in compression between flange 53 and flange 49 with bracket 52 being longitudinally adjust- .able on threaded rod 41 for varying the amount of spring bias supplied on valve 26 and nozzle assembly 34 and with lock nut 55 securing the assembly.

In particular, spring 47 under compression provides a threshold force holding valve 26 in a closed position against a force on the lower exposed face of valve 26 by reason of the water pressure within pipe member 31. With reference to FIG. 3, this water pressure in member 31 is applied to the area of valve 26 circumscribed by opening 32 and when this force exceeds the bias force of spring 47 by reason of the increasing water pressure within accumulator l2, poppet valve 26 is forced upwardly off a valve seat 61 at throat opening 32. Once poppet valve 26 unseats, an additional pressure receptive area is exposed to the accumulated water pressure within member 31 causing the valve to rise very rapidly and carry nozzle assembly 34 with it upwardly to the extended position as shown in FIG. 4. The additional surface area of valve 26 is provided by the lower radially outermost circumferential surfaces 62 of the valve as best illustrated by FIGS. 3 and 4. As indicated above this operation communicates opening 32 with nozzles 37 and 38 effecting a water discharge therefrom with such discharge continuing at varying intensity until the pressure is relieved within member 31 at which time the bias of spring 47 predominates,

forcing assembly 34 and valve 26 to return to the retracted position as shown by FIG. 1.

It is observed that the upper limit of vertical movement of assembly 34 is determined solely by the balancing of the spring force against the water pressure at the throat of member 31. Thus there is no wear or potential breakage due to impact against mechanical limits.

In the retracted position, an O-ring seal assembly, consisting of a valve seat member 60, an O-ring 63 and an O-ring retainer 65, is provided at opening 32 for sealing engagement between a circumferential shoulder 64 formed on the lower surface of poppet valve 26 and O-ring 63 as best illustrated in FIGS. 3 and 4. Additionally, to effect a rapid opening of valve 26 when the water pressure within pipe 21 reaches the threshold level, member 31 is provided with a circumferential flange adjacent throat opening 32 having a vertically extending annular wall 66 rising above and circumferentially surrounding valve seat 61 for inhibiting water leakage between surface 62 and the seat 61' engageable therewith by reason of the corner which water leakage must follow in order to escape. Such leakage which might otherwise occur as the water pressure approaches the thre'shold level, meets the obstacle provided by the circumferential vertical wall 66 and is redirected to apply additional pressure against the lower surface 62 of the valve so as to force it rapidly upwardly to its open position. It is also observed that in accordance with the operation in the present invention, the

.tical guide surfaces slidably engaging an inside annular surface of O-ring retainer 65 at throat opening 32 as illustrated by FIGS. 3 and 4. Pins 71 are of sufficient length so that their lower ends extend below opening 32 when assembly 34 and valve 26 are in their most upwardly extended position, such that upon retraction the pins effectively guide the lower surfaces including shoulder 64 of valve 26 into sealing engagement with the O-ring assembly.

In addition to the vertical reciprocation of nozzle assembly 34 relative to upstanding pipe member 31, the assembly is also rotatable relative to pipe 31 and a rotation indexing means is provided in the form of ratchet means 76 as best shown in FIGS. 8 through 14, carried by nozzle assembly 34 and pipe member 31 for translating each vertical cycle of reciprocation of the assembly into an increment of rotation thereof. In this manner, directional nozzles 37 and 38 discharge jets of water in a laterally or radially outward and upward trajectory, and are indexed circuitely to a new radial direction during each cycle of operation. In particular the indexing ratchet means 76 includes a pawl 77 rotatably mounted to nozzle assembly 34 adjacent a lower edge 78 of sleeve member 36 so as to dispose the pawl in a position for cooperating with a crown ratchet 79 providing a plurality of pawl receiving notches or teeth 81 circumferentially extending about pipe member 31 and fixed relatively thereto by a plurality of bolts 82 mounted in a base flange 83 of pipe member 31. Flange 83 also provides a junction for joining the lower end of pipe member 31 to pipe extension 33 as shown. An axis of rotation 84 for pawl 77 extends in a direction normal to the longitudinal axis of sleeve 36 of nozzle assembly 34 and the pawl is formed with a pair of toes 86 and 87 symmetrically spaced about axis 84 for movement into engagement with teeth 81 of crown ratchet 79. In particular pawl 77 is biased by spring 88 connected between the pawl and nozzle assembly 34 as illustrated to dispose pawl 77 in one or the other of two stable orientations relative to nozzle assembly 34 and teeth 81, each orientation providing incremental rotation of the nozzle assembly in one angular direction or the other.

In the position shown by FIG. 5, pawl 77 is in an orientation in which spring 89 urges toe 86 toward teeth 81. With this orientation in mind and with reference to FIG. 9, as nozzle assembly 34 responds to a threshold discharge pressure, it is driven upwardly to an extended position whereby toe 86 disengages from teeth 81 allowing spring 89 to rotate pawl 77 about axis 87 until an abutment 91 adjacent toe 86 engages a limit stop provided by stub 92 as illustrated in FIGS. and 9. This permits toe 86 to advance its position relative to teeth 81, in this instance moving a notch from left to right as viewed in H0. 5. Subsequent return of assembly 34 toward its retracted position causes toe 86 of pawl 77 to engage teeth 81 at the advanced position as best illustrated in H6. 9 by the phantom representation of pawl 77. Upon completion of the retraction cycle, toe 86 abuts a face 93 of one of teeth 81 at the advanced tooth position causing a camming action forcing axis 84 of pawl 77 and sleeve 36 of the nozzle assembly to rotate from left to right or in a counter clockwise direction when viewed from the top of the assembly. Thus as illustrated by FIG. 9, a vertical upward extension and subsequent retraction of axis 84 of pawl 77 over a distance a is translated into an increment of rotation of an amount b with pawl 77 assuming the position shown by the solid lines in FIG. 9 when nozzle assembly 34 is in its fully retracted position. As described herein, means are provided for moving nozzle assembly 34 back and forth through arcuate segments less than a full 360 of rotation and for this purpose pawl 77 includes the additional toe 87 symmetrically spaced from toe 86 on an opposite side of axis 84 and an additional stop in the form of stud 98. Spring 88 is joined to pawl 77 at connection 93 overlying axis 84 and continuously urges connection 94 of pawl 77 away from a connection 96 to sleeve 36 such that pawl 77 may be shifted from its present position in which toe 86 is urged toward teeth 81 to another stable orientation in which connection 94 on the pawl is to the right of connection 96 so as to urge toe 87 toward teeth 81. This other orientation of pawl 77 is illustrated by FIG. 14 and provides for rotating nozzle assembly 34 in a right to left direction as viewed in FIG. 5 or a clockwise rotation as viewed from the top of the assembly.

One of the features of the present invention is best illustrated in FIG. 9 in which toe 86 with pawl 77 and nozzle assembly 34 in the retracted position is angulated relative to abutment face 93 of teeth 81 so as to provide a slippage angle therebetween for semi-free rotation in the event of accidental rotation of the nozzle assembly. Such rotation, which may for example be inadvertently caused by an eccentric engagement of the wheel ofa vehicle with a top guard plate 97 of assembly 34 can occur in either a clockwise or a counter clockwise direction and with either of toes 86 or 87 engaged with teeth 81. In this manner, damage to the indexing mechanism of sprinkler head 11 is avoided thus providing a distinct advantage over many conventional sprinkler heads and systems in which rotation is achieved by gear mechanisms. Notwithstanding the slip action of pawl 77, the incrementation provided thereby is positive and trouble free. In the p resent embodiment, which provides'a primary jet discharge of up to 100 feet, each increment of rotation provides a 3 positive rotational step such that a uniform distribution of water is achieved over the preselected area to be covered. The 3 step is provided by dividing crown ratchet 79 into equally dimensioned teeth.

Mounted at preselected circumferential locations about said pipe member 31 are a pair of upstanding trip control arms 111 and 112 as best shown in FIGS. 5 and 10 for automatically shifting pawl 77 from one stable orientation to the other. This causes change in the direction of incremental rotation of nozzle assembly 34 at each of the control arms and thereby provide sprinkler head 11 with arcuate discharge patterns less than 360. For example, by disposing the control arms at positions generally from each other as shown for control arms 111 and 112 in FIG. 10, a semicircular discharge pattern for nozzle assembly 34 is achieved. Arms 111 and 112 are in this instance secured by bolts 82 at the 180 opposed locations and with four such bolts 82 as shown, any desired arcuate pattern of one quarter circle (90), half circle rotation (180) or three quarters circle rotation (270) may be obtained merely by selective positioning of arms 111 and 112.

Each of arms 111 and l 12 is formed with a catch portion 113 and 114 respectively defined by the junction of a relatively slender leg 116 and 117 with an upper flange 118 and 119 bent at right angles relative to the legs 116 and 117 of arms 111 and 112 respectively. Catch portions 113 and 114 defined generally downwardly facing abutments turned inwardly toward the arcuate path followed by pawl 77.

During operation, pawl 77 may be disposed with a toe 86 biased by spring 88 so as to cooperate with teeth 81 rotating assembly 34 and pawl 77 in a direction toward control arm 112 as illustrated by FIGS. 10, 11 and 12. Each of the arms, in this instance arm'112, is disposed with the catch portion, in this instance catch portion 114, in the arcuate path of pawl 77 as nozzle assembly 34 rotates pursuant to the incrementation. As pawl 77 approaches arm 1 12, toe 87 opposite the functioning toe 86 moves into engagement with flange 119 and on a downward stroke of assembly 34 toe 86 cams against one of the teeth 81 forcing toe 87 into flange 119 deflecting arm 112 as illustrated in FIG. 12. Control arms 111 and 112 are formed of a spring metal or other material of suitable strength and resiliency and each of these legs is relatively slender to provide an elastic deformation when disposed in the condition of arm 112 as shown in FIG. 12.

Toes 86 and 87 of pawl 77 are in this instance formed by integral tabs 121 and 122 extending outwardly at right angles on opposite sides of axis 84 from a rotatably mounted pawl body 123 and thereby defining generally upwardly facing shoulders 126 and 127 engageable with catch portions 113 and 114 of the control arms respectively. In particular, with reference to FIGS. 12. and 13 as assembly 34 completes its downward stroke into the retracted position toe 87 engages flange 119 and deflects arm 112 until toe 87 slides under flange 119 allowing arm 112 to return to its generally upright disposition disposing catch portion 114 above shoulder 127 of tab 122. Subsequently on the next upward storke or extension of assembly 34 as shown by FIG. 14, catch portion 114 engages shoulder 127 of the pawl, restraining toe 87 from further upward movement and thus tripping the pawl to a position as illustrated by FIG. 14. Toe 87 is thus biased toward teeth 81 for incrementing assembly 34 in a right to left hand direction or clockwise rotation as viewed from the top. The same tripping function occurs at the other end of the arcuate path this time with shoulder 126 cooperating with catch portion 113 of control arm 111.

With reference to FIGS. 1 and each of the sprinkler units including a pressure actuated head 11, and accumulator 12 and a flow control valve 14, is adapted to be installed below a grade level 131 to recess the various components, so as not to obstruct or interfere with the use of the grounds. For this purpose, each sprinkler head 11 is provided with an annular guard skirt 132 here having the shape of an inverted truncated cone with the truncated end being disposed circumferentially about and fixed to a lower end of the pipe member 31 and in this instance being an integral casting portion of pipe extension 33. Guard skirt 132 thus slopes upwardly and outwardly from its secured truncated end to define an upper rim 133 which is adapted for disposition at or slightly above grade level 131 as shown by FIGS. 1 and 5. During installation the conduit leading to pipe extension 33, in this instance conduit 134 is positioned relative to grade level 131 such that guard skirt 132 and pipe extension 33 when threadedly secured to conduit 134 disposes rim 133 as shown substantially at grade level. In this manner guard skirt 132 retains the surrounding soil or grade material from interfering with nozzle assembly 34 or the indexing mechanism associated therewith. Pipe member 31 extends upwardly from section 33 and thus from the lower end of guard skirt 132 to throat opening 32 which is vertically spaced below rim 133 of the guard skirt such that nozzle assembly 34 assumes in its retracted position a disposition substantially as shown by FIG. 1 in which the upper enclosed end 39 of assembly sleeve member 36 is just slightly below grade level 131. Nozzle assembly 34 carries at the upper end thereof a cover or guard plate 97 having a circular periphery and suitably fastened by means such as screws 136 to a raised circumferential wall 137 of sleeve member 36 adjacent enclosed end 39 as illustrated with raised wall 137 cooperating with a recess 138 in plate 97 to provide clearance for nut 42 and a lock screw 139. The perimeter of plate 97 is shaped to matingly seat with rim 133 as shown at 141 providing further protection of nozzle assembly 34 against debris or the like and forming a generally flat horizontal platform substantially coplanar with the surrounding grade level 131 and flush with guard skirt rim 133 when nozzle assembly 34 is in its retracted position. Plate 97 has in this instance a notched portion 140 adjacent the perimeter thereof and overlying nozzle 37 for clearance of the jet discharge therefrom.

During installation, following the placement of pipe extension 33 and integral guard skirt 132, upstanding pipe member 31 may be disposed in place and secured together with crown ratchet 79 and control arms 111 and 112 by means of bolts 82 extending through and securing base flange 83 of member 31 to a circumferential seat formed by the connection of skirt 132 to the pipe extension 33. An annular seal 142 is disposed between flange 83 and the circumferential seat defined by extension 33 and guard skirt 132. Thereafter nozzle assembly 34 may be mounted in place and with guard plate 97 removed, nut 42 and lock screw 139 may be installed to secure assembly 34 to rod 41 and valve 26 as shown in FIG. 4. Finally guard plate 97 may be mounted in place.

It is observed that by this construction, pipe extension 33 serves to house the lower half of spring 47 and bracket 52 and moreover to guide bracket 52 in its vertical reciprocation by means of splines 143 formed longitudinally on the interior wall of pipe section 33. The outer peripheral edge of annular flange portion 53 thus slidably engages splines 143 as best shown by FIG. 8.

Further in accordance with the present invention nozzle assembly 34 is comprised of a primary nozzle 37 having a discharge passage 146 extending through sleeve 36 in a direction radially outwardly therefrom sloping upwardly from the horizontal to define a trajectory for a primary discharge stream 147 having a trajectory angle of about 30 from the horizontal for efficient water coverage by the discharge. Passage 146 is formed with a plurality of longitudinal vanes 148 and a tapered nozzle portion 149 for forming jet stream 147 with the tapered portion 149 being defined by a removable plastic nose piece 151.

It is observed in connection with primary nozzle 37 that discharge head 11 functions in combination with a precharged accumulated 12 for maximum efficiency. In particular accumulator 12 is precharged in upper chamber 22 with a gas pressure of approximately 60 psi via access hole 153 and a normally secured valve means 154 communicating with upper chamber 22. Relative to this precharge pressure of 50 to psi, spring 47 is selected to provide when adjusted by bracket 52, a threshold valve opening or discharge pressure of to psi. This relatively high operating pressure range for head 11, available by virture of the prechargeable accumulator 12, permits primary nozzle 37 to operate most efficiently. Nozzles operating under lower pressure limits do not provide sufficient stream breakup which in turn results in relatively large drops of water causing turf damage and the like by reason of the heavy impact. Efficient stream breakup as provided by the present invention results in a finer spray and more effective irrigation.

In this instance accumulator 12 is provided with a diaphram which prevents absorbtion of the gas into the water. with the lower chamber 23 filled with water, immediately prior to discharge, diaphram 20 assumes a disposition as shown in phantom in FIG. 1, and the gas in the upper chamber 22 is at or approaching its highest pressure in the cycle of operation. A suitable accumulator for this purpose is available from Greer Olaver Product Division of Greer Hydraulics, Inc., Los Angeles, Calif.

Another aspect of the present invention is the disposition of a secondary nozzle 38 extending parallel to and underlying nozzle 37 and having a substantially smaller discharge passage 156 relative to the dimensions of passage 146. With reference to FIGS. 4 and 5, secondary nozzle 38 provides a secondary stream 157 which is in this instance moderately broken up by a finger 158 carried by nozzle 38 at the opening of passage 156, for providing water delivery to the ground areas close to head 11. Stream 147 which provides effective coverage at greater distances is not efficient for those areas immediately surrounding the head. The close-in coverage of secondary nozzle 38 is aided by an orientation of nozzle 38 in accordance with the present invention by which stream 157 thereof is intercepted by rim 133 of skirt 132 during downward retraction of assembly 34 as best shown in FIG. 5 to cause a dispersion of stream 157 as shown at 159 for effective close-in water delivery.

An important function of this placement of nozzle 38 is to achieve a partial evacuation of water which unavoidably and undesirably accumulates in the bowl region defined by skirt 132 and which but for the action of nozzle 38 would cause a water puddle surrounding head 11. In particular, stream 157 during the downward stroke of assembly 34 causes a venturi-like effect adjacent the upper regions of skirt 132, thus pulling the water from this upper region and dispersing it at 159 such that the accumulated water assumes a level approximately as shown at 161 when the assembly is fully retracted. The evacuated upper region thus provides sufficient air space for the retraction of assembly 34 without causing a plunging action forcing water to spill over rim 133 and flood the surrounding area.

Although accumulation of water within skirt 132 has been found generally unavoidable, it is to a certain extent minimized by the provision of an annular seal 162 fixedly carried by an interior wall of sleeve member 36 and slidable relative to an exterior surface of pipe member 31 so as to discourage leakage of water from the lower end of sleeve member 36 during discharge when nozzle assembly 34 is in its extended position. Accompanying annular seal 162 are a pair of annular bearings 163 and 164 each in this instance provided by a cylindrical section of Teflon (Trademark owned by Du Pont) material mounted within annular recesses of sleeve member 36 as shown in FIG. 4.

Accordingly, any number of sprinkler units may be provided, as units 16, 17 and 18 as shown by FIG. 1 and connected to a common source of water in this instance via supply line 13. Each of the units may be separately adjusted for individualized water coverage by changing the precharge pressure on accumulator l2, adjusting the compression force in spring 47 to change the threshold discharge pressure of head 11 or by changing the size of flow control valve 14. Typically it will be desirable to provide a pressure on line 13 of approximately 100 to I20 psi so as to meet the threshold discharge pressure of each of the sprinkler heads. This may be provided by a pump 166 connected to a water main at a pressure substantially lower than 100 psi (not shown) and operated by suitable control means which in this instance is shown by timer 167. With this arrangement pump 166 provides sufficient pressure at a relatively low flow rate sufficient for example to supply each sprinkler unit with 3 to 4 gallons per minute, over line 13 to the accumulators, accumulator 12 for unit l6, 12 for unit 17 and 12" for unit 18, through individual flow control valves 14 for unit l6, 14 for unit 17 and 14" for unit 18. Each of the pressure actuated discharge heads, head 11 for unit 16 and heads 11' and 11" for units 17 and 18, responds to the accumulation of water within each of the respective accumulators to intermittently discharge the built-up water pressure in accordance with the more detailed description set forth above. For a typical precharge pressure in each of the accumulators of 60 psi, corresponding to the pressure at which the valve returns to its retracted or closed condition following a discharge and a threshold discharge pressure of 100 psi, at which the valve opens, the cyclic rate ofthe present embodiment of head 11 is three discharges per minute, each discharge lasting for approximately one half of a second. With this embodiment of the invention operating with these pressures, a discharge range of up to feet is achieved for th stream discharged by primary nozzle 37.

It is observed in connection with the overall operation of the system that the various discharge heads do not produce undesirable water hammer effects on the supply line. Each head opens in response to the rising pressure in the associated accumulator and commences to close smoothly as the increasing restorative force of spring 47 overcomes the decreasing water pressure against valve 29 at throat opening 32. Thus the sprinkler system in accordance with the present invention does not strain the supply line and pumping equipment with repeated water hammer effects each time the various heads operate.

I claim:

1. A pressure actuated intermittent discharge sprinkler comprising:

an elongated pipe member having a throat opening at one end and adapted at its other end for connection to a source of water under pressure,

a nozzle assembly slidably and rotatably mounted on said pipe member for reciprocation between retracted and extended positions and having a nozzle for communication with said pipe member throat opening,

valve means carried by said nozzle assembly and movable therewith between the retracted position closing said throat opening of said pipe member and the extended position communicating said nozzle and throat opening for water discharge,

bias means urging said nozzle assembly and valve means to said retracted position such that water under pressure in said pipe member may overcome said bias means forcing said valve and assembly to said extended position until pressure is relieved by discharge through said nozzle, and

a rotation indexer including ratchet means carried by said nozzle assembly and pipe member translating each cycle of assembly reciprocation into an increment of rotation thereof.

2. The sprinkler of claim 1, wherein said nozzle assembly is comprised of a sleeve member having an open end slidably and rotatably mounted on said upstanding pipe member and a closed opposite end, said nozzle having a discharge passage adjacent said closed end extending through said sleeve member and radially outwardly therefrom to provide water discharge when said nozzle assembly is in its extended position.

3. The sprinkler of claim 3, wherein said valve means is carried within said nozzle assembly sleeve member underlying the closed end thereof for cooperation with the throat opening of said pipe member, and said bias means is provided by an elongate coil spring coaxially disposed within said pipe member with an upper end of said spring abutting a downwardly facing circumferential flange of said pipe member underlying said throat opening with a lower end connected to said valve means by a linkage means upwardly extending therefrom through the throat opening to said valve means, whereby said spring is placed in compression so as to urge said valve means and nozzle assembly into said retracted position.

4. The sprinkler of claim 3, wherein said valve means has an annular poppet valve member and said pipe member throat opening is annular and provides a valve seat matingly receiving said valve member, said valve member fixedly carrying a plurality of downwardly depending circumferentially spaced guide pins defining vertical guide surfaces for limiting eccentric movement of the valve member relative to the inside annular surface of said throat opening.

5. The sprinkler of claim 1, wherein said indexer comprises a pawl rotatably mounted on said nozzle assembly and said pipe member has affixed thereto a ring of pawl receiving teeth circumferentially extending about said pipe member in cooperative relation with said pawl when said nozzle assembly is in the retracted position, means for rotation of said pawl in response to upward extension of said assembly to advance a tooth engaging toe of said pawl relative to said ring of teeth such that subsequent movement of said assembly toward said retracted position moves said pawl toe into engagement with said ring of teeth at the advanced position effecting an increment of rotation of said nozzle assembly upon completion of the retraction thereof.

6. The sprinkler of claim 5, wherein said indexer is further defined by said axis of pawl rotation being normal to the axis of said nozzle assembly and said pawl having a pair of teeth engaging toes symmetrically oriented at spaced positions relative to the axis of rotation thereof, spring bias means connected between said pawl and nozzle assembly biasing said pawl in one or the other of two selectable stable orientations and providing said means for pawl rotation, each pawl orientation providing a different direction of incremental rotation in response to vertical reciprocation of said nozzle assembly, and direction control means fixedly disposed LII relative to said pipe member for automatically tripping said pawl from one stable orientation to the other at preselected circumferential locations about said pipe member, whereby said nozzle discharge is automatically incrementally rotated in selected arcuate paths.

7. The sprinkler of claim 6, said indexer being further defined by said pawl toes being positioned on opposite sides of the axis of rotation thereof and said spring bias continuously urging rotation of one or the other of said toes toward engagement with said ring of teeth,

stop means fixedly carried by said nozzle assembly limiting rotation of said pawl during upward extension of said assembly to dispose one of the other of said toes in said advanced position relative to said ring of teeth.

8. The sprinkler of claim 7, said control means for tripping said pawl comprising:

a pair of pawl engaging control arms fixedly mounted relative to said pipe member at spaced circumferential locations, and each arm having catch portions disposed in the arcuate path of said pawl, said pawl being formed with a shoulder adjacent each toe individually cooperating with each arm at the ends of said arcuate path to be engaged by said catch portion such that vertical reciprocation of said nozzle assembly trips said pawl from one stable orientation to the other.

9. A system of pressure actuated intermittent discharge sprinkler units connected to a common water source, each sprinkler unit comprising:

an accumulator adapted for connection to said water source for accumulating water under increasing pressure,

a pressure actuated water delivery head including a normally closed valve means, said head connected to said accumulator and said valve means being responsive to an increasing water pressure therein to intermittently discharge water to relieve the pressure in said accumulator and resume its normally closed condition, and

a self-adjusting flow control valve connecting said accumulator to said source of water such that periodic build-up and relief of pressure therein is not communicated to said source and thus does not adversely influence operation of the remaining sprinkler units connected thereto.

10. In the system of claim 9, the provision in each sprinkler unit of:

an upstanding pipe member having a throat opening at an upper end and connected at an lower end to said accumulator,

a nozzle assembly slidably and 'rotatably mounted on said pipe member for vertical reciprocation between retracted and extended positions and having a directional nozzle for communicating with said throat opening, said valve means carried by said nozzle assembly and movable therewith downwardly to the retracted position to close said throat opening of said pipe member and movable upwardly to the extended position communicating said nozzle and said throat opening, spring bias means urging said nozzle assembly and valve means to said retracted position such that the intermittent opening is accompanied by upward movement of said nozzle assembly to said extended position until the pressure of water in said accumulator is relieved by discharge through said nozzle.

11. In the system of claim 10, each sprinkler unit head further comprising a rotation indexer including ratchet means carried by said nozzle assembly and said pipe member, said indexer translating each vertical cycle of assembly reciprocation into an increment of rotation thereof.

12. A pressure actuated periodic discharge sprinkler for subgrade installation comprising:

a pipe member for vertical disposition below a grade level and having a throat opening at an upper end thereof,

an annular guard skirt fixedly mounted with and coaxially surrounding said pipe member adjacent said throat opening and having an upper rim for disposition substantially at grade level,

a nozzle assembly slidably and rotatably mounted on said pipe member for vertical reciprocation between retracted and extended positions and having a nozzle for communication with said pipe throat opening, said nozzle assembly including a horizontally mounted generally circular guard plate overlying said nozzle and disposed to assume a substantially flush relation with said guard skirt upper rim when said assembly is in its retracted position,

valve means carried by said nozzle assembly and movable therewith downwardly to a retracted position closing said throat opening of said pipe member and movable upwardly to the extended position communicating said nozzle and throat opening, and

spring bias means urging said nozzle assembly and valve means to said retracted position such that water under pressure in said pipe member overcomes the force of the bias means, forcing said valve means and assembly to said extended position with said guard plate and nozzle rising above the rim of said skirt for nozzle clearance and water discharge until pressure is relieved.

13. The sprinkler of claim 12, wherein said nozzle of said assembly is a primary nozzle having a relative large discharge passage and further comprising a secondary nozzle underlying said primary nozzle and having a relatively smaller discharge passage extending generally parallel to said primary nozzle passage, said secondary nozzle passage being disposed on said nozzle assembly such that a jet of water discharge therefrom during downward movement of said assembly toward its retracted position is intercepted by an upper edge of said guard skirt rim causing radially outward spray deflection of the secondary nozzle discharge jet and partially evacuating accumulated water in an upper cavity region of said guard member by a venturi action.

14. The sprinkler of claim 12, wherein said guard skirt member is in the shape of an inverted truncated cone with the truncated end circumferentially secured to said pipe member at a location spaced below said throat opening and upwardly extending therefrom to define said rim.

15. The invention as defined in claim 12 wherein said pipe member is connected to a source of pressurized liquid, and including an accumulator and a conduit communicating the accumulator with said pipe member.

16. The invention as defined in claim 15 including flow control means between said source and the conduit.

17. The invention as defined in claim 16 wherein said flow control means comprises a self-adjusting valve having an opening therethrough, the effective size of the opening varying in general inverse relation to the difference of liquid pressure across the opening.

18. The invention as defined in claim 15 wherein said accumulator includes upper and lower variable volume chambers separated by fluid impermeable means movable to change the volumes of the chambers, the upper chamber being charged with a pressurized gas and the lower chamber being connected to said conduit. 

1. A pressure actuated intermittent discharge sprinkler comprising: an elongated pipe member having a throat opening at one end and adapted at its other end for connection to a source of water under pressure, a nozzle assembly slidably and rotatably mounted on said pipe member for reciprocation between retracted and extended positions and having a nozzle for communication with said pipe member throat opening, valve means carried by said nozzle assembly and movable therewith between the retracted position closing said throat opening of said pipe member and the extended position communicAting said nozzle and throat opening for water discharge, bias means urging said nozzle assembly and valve means to said retracted position such that water under pressure in said pipe member may overcome said bias means forcing said valve and assembly to said extended position until pressure is relieved by discharge through said nozzle, and a rotation indexer including ratchet means carried by said nozzle assembly and pipe member translating each cycle of assembly reciprocation into an increment of rotation thereof.
 2. The sprinkler of claim 1, wherein said nozzle assembly is comprised of a sleeve member having an open end slidably and rotatably mounted on said upstanding pipe member and a closed opposite end, said nozzle having a discharge passage adjacent said closed end extending through said sleeve member and radially outwardly therefrom to provide water discharge when said nozzle assembly is in its extended position.
 3. The sprinkler of claim 3, wherein said valve means is carried within said nozzle assembly sleeve member underlying the closed end thereof for cooperation with the throat opening of said pipe member, and said bias means is provided by an elongate coil spring coaxially disposed within said pipe member with an upper end of said spring abutting a downwardly facing circumferential flange of said pipe member underlying said throat opening with a lower end connected to said valve means by a linkage means upwardly extending therefrom through the throat opening to said valve means, whereby said spring is placed in compression so as to urge said valve means and nozzle assembly into said retracted position.
 4. The sprinkler of claim 3, wherein said valve means has an annular poppet valve member and said pipe member throat opening is annular and provides a valve seat matingly receiving said valve member, said valve member fixedly carrying a plurality of downwardly depending circumferentially spaced guide pins defining vertical guide surfaces for limiting eccentric movement of the valve member relative to the inside annular surface of said throat opening.
 5. The sprinkler of claim 1, wherein said indexer comprises a pawl rotatably mounted on said nozzle assembly and said pipe member has affixed thereto a ring of pawl receiving teeth circumferentially extending about said pipe member in cooperative relation with said pawl when said nozzle assembly is in the retracted position, means for rotation of said pawl in response to upward extension of said assembly to advance a tooth engaging toe of said pawl relative to said ring of teeth such that subsequent movement of said assembly toward said retracted position moves said pawl toe into engagement with said ring of teeth at the advanced position effecting an increment of rotation of said nozzle assembly upon completion of the retraction thereof.
 6. The sprinkler of claim 5, wherein said indexer is further defined by said axis of pawl rotation being normal to the axis of said nozzle assembly and said pawl having a pair of teeth engaging toes symmetrically oriented at spaced positions relative to the axis of rotation thereof, spring bias means connected between said pawl and nozzle assembly biasing said pawl in one or the other of two selectable stable orientations and providing said means for pawl rotation, each pawl orientation providing a different direction of incremental rotation in response to vertical reciprocation of said nozzle assembly, and direction control means fixedly disposed relative to said pipe member for automatically tripping said pawl from one stable orientation to the other at preselected circumferential locations about said pipe member, whereby said nozzle discharge is automatically incrementally rotated in selected arcuate paths.
 7. The sprinkler of claim 6, said indexer being further defined by said pawl toes being positioned on opposite sides of the axis of rotation thereof and said spring bias continuously urging rotation of one or the other of said toes toward engagemenT with said ring of teeth, stop means fixedly carried by said nozzle assembly limiting rotation of said pawl during upward extension of said assembly to dispose one of the other of said toes in said advanced position relative to said ring of teeth.
 8. The sprinkler of claim 7, said control means for tripping said pawl comprising: a pair of pawl engaging control arms fixedly mounted relative to said pipe member at spaced circumferential locations, and each arm having catch portions disposed in the arcuate path of said pawl, said pawl being formed with a shoulder adjacent each toe individually cooperating with each arm at the ends of said arcuate path to be engaged by said catch portion such that vertical reciprocation of said nozzle assembly trips said pawl from one stable orientation to the other.
 9. A system of pressure actuated intermittent discharge sprinkler units connected to a common water source, each sprinkler unit comprising: an accumulator adapted for connection to said water source for accumulating water under increasing pressure, a pressure actuated water delivery head including a normally closed valve means, said head connected to said accumulator and said valve means being responsive to an increasing water pressure therein to intermittently discharge water to relieve the pressure in said accumulator and resume its normally closed condition, and a self-adjusting flow control valve connecting said accumulator to said source of water such that periodic build-up and relief of pressure therein is not communicated to said source and thus does not adversely influence operation of the remaining sprinkler units connected thereto.
 10. In the system of claim 9, the provision in each sprinkler unit of: an upstanding pipe member having a throat opening at an upper end and connected at an lower end to said accumulator, a nozzle assembly slidably and rotatably mounted on said pipe member for vertical reciprocation between retracted and extended positions and having a directional nozzle for communicating with said throat opening, said valve means carried by said nozzle assembly and movable therewith downwardly to the retracted position to close said throat opening of said pipe member and movable upwardly to the extended position communicating said nozzle and said throat opening, spring bias means urging said nozzle assembly and valve means to said retracted position such that the intermittent opening is accompanied by upward movement of said nozzle assembly to said extended position until the pressure of water in said accumulator is relieved by discharge through said nozzle.
 11. In the system of claim 10, each sprinkler unit head further comprising a rotation indexer including ratchet means carried by said nozzle assembly and said pipe member, said indexer translating each vertical cycle of assembly reciprocation into an increment of rotation thereof.
 12. A pressure actuated periodic discharge sprinkler for subgrade installation comprising: a pipe member for vertical disposition below a grade level and having a throat opening at an upper end thereof, an annular guard skirt fixedly mounted with and coaxially surrounding said pipe member adjacent said throat opening and having an upper rim for disposition substantially at grade level, a nozzle assembly slidably and rotatably mounted on said pipe member for vertical reciprocation between retracted and extended positions and having a nozzle for communication with said pipe throat opening, said nozzle assembly including a horizontally mounted generally circular guard plate overlying said nozzle and disposed to assume a substantially flush relation with said guard skirt upper rim when said assembly is in its retracted position, valve means carried by said nozzle assembly and movable therewith downwardly to a retracted position closing said throat opening of said pipe member and movable upwardly to the extended position communicating said nozzle and throat opening, and spring bias means urging said nozzle assembly and valve means to said retracted position such that water under pressure in said pipe member overcomes the force of the bias means, forcing said valve means and assembly to said extended position with said guard plate and nozzle rising above the rim of said skirt for nozzle clearance and water discharge until pressure is relieved.
 13. The sprinkler of claim 12, wherein said nozzle of said assembly is a primary nozzle having a relative large discharge passage and further comprising a secondary nozzle underlying said primary nozzle and having a relatively smaller discharge passage extending generally parallel to said primary nozzle passage, said secondary nozzle passage being disposed on said nozzle assembly such that a jet of water discharge therefrom during downward movement of said assembly toward its retracted position is intercepted by an upper edge of said guard skirt rim causing radially outward spray deflection of the secondary nozzle discharge jet and partially evacuating accumulated water in an upper cavity region of said guard member by a venturi action.
 14. The sprinkler of claim 12, wherein said guard skirt member is in the shape of an inverted truncated cone with the truncated end circumferentially secured to said pipe member at a location spaced below said throat opening and upwardly extending therefrom to define said rim.
 15. The invention as defined in claim 12 wherein said pipe member is connected to a source of pressurized liquid, and including an accumulator and a conduit communicating the accumulator with said pipe member.
 16. The invention as defined in claim 15 including flow control means between said source and the conduit.
 17. The invention as defined in claim 16 wherein said flow control means comprises a self-adjusting valve having an opening therethrough, the effective size of the opening varying in general inverse relation to the difference of liquid pressure across the opening.
 18. The invention as defined in claim 15 wherein said accumulator includes upper and lower variable volume chambers separated by fluid impermeable means movable to change the volumes of the chambers, the upper chamber being charged with a pressurized gas and the lower chamber being connected to said conduit. 